This invention relates to a method for the manufacture of high-strength sintered articles composed preponderantly of silicon nitride or .beta.'-Sialon which has the .beta.-silicon nitride structure.
Sintered articles formed preponderantly of Si.sub.3 N.sub.4 enjoy the properties of high thermal resistance, high strength, and a low thermal expansion coefficient. Owing to these properties, they have been drawing keen interest and have found utility in applications to automobile engine parts, gas turbine parts, cutting tools, etc. There are persistent efforts at adoption of compounds based on Y.sub.2 O.sub.3 -Al.sub.2 O.sub.3, MgO, and Al.sub.2 O.sub.3 -MgO as sintering aids capable of enhancing strength and heightening density in the sintered articles of Si.sub.3 N.sub.4. Unfortunately, incorporation of these sintering aids has failed to enhance the strength of the sintered articles sufficiently.
Sintered articles formed preponderantly of .beta.'-Sialon exhibit advantageous properties such as high thermal resistance and ability to retain high mechanical strength, high wear resistance, high resistance to oxidation, and a low thermal expansion coefficient at elevated temperatures. Owing to these properties, they have been attracting deep interest and encouraging trial adoption of the sintered articles in ceramic parts for thermal engines such as automobile engines and gas turbines, in corrosion proof materials, and in refractories for molten metals.
By the term ".beta.'-Sialon" used herein is meant a solid solution of oxynitride having an Si-Al-O-N based composition and possessing a three-dimensional network structure similar to the structure of .beta.-Si.sub.3 N.sub.4. This substance has a composition represented by the general formula, Si.sub.6-Z Al.sub.Z O N.sub.8-Z (wherein, 0.0.ltoreq.Z.ltoreq.4.2 is satisfied).
Heretofore, various methods have been proposed for the manufacture of sintered articles of .beta.'-Sialon. These methods have been unable to produce sintered articles of .beta.'-Sialon with high density, so that the products obtained thereby have failed to manifest the aforementioned merits of .beta.'-Sialon to any appreciable extent.
An object of this invention is to provide a method for the manufacture of sintered articles of .beta.-silicon nitride compositions which enjoy high strength and high density.